An intervertebral disk may suffer degeneration as a result of injury, wear and disease, in which case it often exerts pressure on the nerve fibers of the spinal cord. This can cause severe pain or numbness in the extremities, and even symptoms of paralysis. It may therefore become necessary to remove the degenerated intervertebral disk. However, contact between the vertebrae still has to be avoided, since pain is otherwise caused by the friction between the end-plates of the vertebrae. There may also be medical grounds for avoiding in future a relative movement of the vertebrae that adjoin the degenerated intervertebral disk. In these cases, the degenerated intervertebral disk is replaced by an intervertebral fusion implant, which prevents a relative movement of the vertebrae.
Known intervertebral fusion implants have bearing bodies for placing on the end-plates of an upper and a lower vertebra. They are either inserted directly between the end-plates of two vertebrae or into grooves that have been drilled into the end-plates, with bone substance of the vertebrae being removed. The known implants fuse the two vertebrae bearing on them directly after the implantation. A disadvantage of these implants is that the patient suddenly has to adjust to the limited mobility of his spinal column. On the one hand, he notices the limitation through the implant. On the other hand, his locomotor apparatus also has to adapt immediately to the new situation. Thus, even directly after the operation, the ligaments and muscles of the spinal column are still designed to move the two fused vertebrae. In the period after the operation, this can prolong the phase of acclimatization and rehabilitation of the patient. Moreover, in the phase of acclimatization, the implant is exposed to greater mechanical loads than afterward.